1. Field of the Invention
The present invention relates to lens apparatuses performing AF (autofocus) control.
2. Description of the Related Art
In recent years, automatic focusing function (referred to in the following as “AF”) has become indispensable in image-pickup apparatuses, such as consumer video cameras, broadcast cameras and professional cameras. The most common approach for AF systems is to extract a signal corresponding to the sharpness of an object based on the image-pickup signal, and to evaluate this signal to detect the focusing state of the optical system.
An example of the operation of this AF approach is described with reference to FIG. 8. In FIG. 8, numerical reference 31 denotes an exchangeable lens apparatus, numerical reference 21 denotes a camera, and numerical reference 34 denotes a camera cable.
In the camera 21, numerical reference 211 denotes an image-pickup device, numerical reference 212 denotes an amplifying circuit that amplifies the output of the image-pickup device 211, and numerical reference 213 denotes a processing circuit that processes signals that have been amplified by the amplifying circuit 212 and formats them as NTSC or PAL signals or the like.
Numerical reference 214 denotes a video output terminal that outputs the video signal that is output from the processing circuit 213. Numerical reference 216 denotes a sharpness evaluation value generating circuit that receives the output of the amplifying circuit 212, extracts the sharpness of the video signal from that signal, and generates a sharpness evaluation signal.
Numerical reference 215 denotes a camera-side interface (IF) that creates and transmits various kinds of control information that are necessary for the lens control, such as the AF evaluation value that is output by the sharpness evaluation value generating circuit 216.
In the lens apparatus 31, numerical reference 311 denotes a lens-side IF that receives the control information and the sharpness evaluation value that are output from the camera-side IF 215 via the camera cable 34.
Numerical reference 313 denotes an evaluation value peak searching circuit that generates a signal driving a motor 314 such that the sharpness evaluation value that is successively input from the lens-side IF 311 at the vertical synchronization takes on a peak value.
The motor 314 is actuated by a motor driving signal from the evaluation value peak searching circuit 313, and numerical reference 315 denotes a focus lens that is moved in the optical axis direction by rotating the motor 314.
A light flux that has passed through the focus lens 315 is formed an image on an image-pickup plane of the image-pickup device 211. A signal that has been photo-electrically converted by the image-pickup device 211 is subjected to a sample-and-hold process and is input into the amplifying circuit 212. The amplifying circuit 212 amplifies the signal to a suitable level, and inputs it into the processing circuit 213 and the sharpness evaluation value generating circuit 216. The processing circuit 213 formats the input signal into a video format such as NTSC or PAL, and outputs it to the video output terminal 214. On the other hand, the sharpness evaluation value generating circuit 216 filters the signal that has been input, generates, at each vertical synchronization period, a digital evaluation signal that indicates the sharpness of the video signal from frequency components included in the video signal, and outputs it as a sharpness evaluation value to the camera-side IF 215.
The camera-side IF 215 transmits to the lens apparatus 31 with this evaluation value and other information necessitated by the lens apparatus 31
The lens-side IF 311 outputs the received information to the circuits within the lens apparatus 31, and outputs for example the sharpness evaluation value to the evaluation value peak searching circuit 313. The evaluation value peak searching circuit 313 generates a driving signal for the motor 314, and searches the position of the focus lens 315 at which the sharpness evaluation value takes on a peak, while driving the motor 314 and comparing the sharpness evaluation values that are input into it at each vertical synchronization period.
It should be noted that the video AF operation of camera systems employing this structure is discussed in detail in Japanese Patent Laid-Open Nos. H9(1997)-9130, H9(1997)-9131 and H9(1997)-9132 (corresponding to U.S. Pat. No. 6,373,524).
On the other hand, ordinary camera systems for broadcasting or professional use are connected with a 12-pin or 36-pin camera cable 34 for serial or parallel communication to exchange the control information that is necessary for the lens control.
In order to communicate the sharpness evaluation value between the lens apparatus 31 and the camera 21 by serial transmission, strict compatibility between the lens apparatus 31 and the camera 21 is required. For this reason, in cases in which the lens apparatus 31 and the camera 21 are supplied by different manufacturers, as is often the case with broadcasting or professional camera systems, it has to be ensured that the interfaces of the different manufacturers are compatible with one another.
However, it is difficult to promote a uniform standard, because signals necessary for the AF operation, such as the sharpness evaluation value, are what is most characteristic of the autofocus operation of each camera manufacturer.